2D-NMR Characterization of Sequence Distributions in the Backbone of Poly(vinylidene fluoride-<i>co</i>-tetrafluoroethylene)

Abstract

NMR is a powerful tool to study the microstructures of poly­(vinylidene fluoride-<i>co</i>-tetrafluoroethylene), poly­(VDF-<i>co</i>-TFE). This study shows that the microstructures in this copolymer can be established completely on the basis of 2D-NMR, in which improved dispersion is achieved by the second dimension (¹⁹F or ¹³C chemical shifts). 2D-NMR has been proven to be extremely effective for identifying the carbon sequence distributions in the polymer main chain. For lower level sequences (3- or 5-carbon sequences), resonance assignments on the basis of one- and two-bond ¹⁹F­{¹³C} gradient heteronuclear single quantum coherence (gHSQC) experiments are in good agreement with assignments obtained by traditional methods. Higher level sequences (7- or 9-carbon sequences), which can not be assigned unambiguously by traditional methods, were determined by ¹⁹F–¹⁹F gradient double quantum correlation spectroscopy (gdqCOSY), which provides ¹⁹F–¹⁹F correlations over 3–5 bonds. A quantitative study was also conducted on the composition of this copolymer. Three different approaches were used to calculate the fraction of TFE and the inversion ratio of VDF units